This invention relates to industrial heat recuperators, and more particularly relates to a heat recuperative apparatus employing a composite ceramic cross-flow heat recuperator for use on furnaces, calciners, ovens and preheaters.
Recent concern about energy conservation and rising fuel costs has caused renewed interest in industrial recuperators to recover waste heat losses and to preheat incoming combustion air to increase the efficiency of furnaces, calciners, ovens and preheaters.
While such recuperators are usually constructed from metal parts, the ceramic recuperator has several advantages over conventional metallic recuperators. For example, ceramics in general have high corrosion resistance, high mechanical strength at elevated temperatures, low thermal expansion coefficients (TEC'S) and good thermal shock resistance, and thus exhibits excellent endurance under thermal cycling; are light in weight (about 1/3 the weight of stainless steel); and are cost competitive with high temperature alloys.
Furthermore, ceramic recuperators are available in a variety of shapes, sizes, hydraulic diameters, (hydraulic diameter is a measure of cross-sectional area divided by wetted perimeters) and compositions. Because their TEC'S are typically lower than those of most metals and alloys, however, ceramic recuperators present a compatibility problem to the design engineer desiring to incorporate them into existing furnace, calciner, oven and preheater structures.
In co-pending U.S. patent application Ser. No. 686,040, filed May 13, 1976, and assigned to the present assignee, there is described a cross-flow ceramic recuperator employing a single ceramic composition. The relatively high cell density of the disclosed structures (for example, 125 cells per square inch) enabled use of such recuperators in forced draft applications, permitting relatively small hydraulic diameters. Where larger hydraulic diameters and/or larger size recuperators are desired (for example, in natural draft applications where back pressures on the order of 0.1 inch of water are desired), fabrication problems are encountered. For example, consideration has been given to assembling large recuperator structures by building them up from blocks or sections of smaller size. However, an attendant problem has been leakage of the heat transfer fluids between subsections or component parts, resulting in the decreased overall efficiency of the recuperative apparatus.